The present invention relates to a method and apparatus to perform ultrasound image acquisition for diagnostic or intervention using a robot to position the ultrasound transducer.
Ultrasound as a medical imaging modality has a number of benefitsxe2x80x94it is inexpensive, non-invasive, real-time, etc. It is used widely for diagnosis, and also in interventions, for example, to guide needles or other instruments for anaesthesis and surgery.
Medical ultrasound examinations often require that ultrasound technicians hold the transducer probe in one hand while adjusting scanning parameters with the other hand, or hold the transducer in awkward positions for prolonged periods of time, sometimes exerting large forces for prolonged periods of time. Not surprisingly, a number of studies indicate that the technicians suffer from an unusually high incidence of musculoskeletal disorders (e.g. Vanderpool, 1993, Craig, 1985).
The use of a robot in conjunction with ultrasound imaging has been described in U.S. Pat. No. 5,817,022, Vesely et al., that discloses a system that enables the display of 2-D ultrasound images in a 3-D viewing environment. The use of a robot to position a surgical/medical intervention instrument under computer control is discussed as an option, but the ultrasound transducers described in that method are fixed. The role of the operator, position or force sensors of ultrasound image in the positioning of the instrument is not discussed.
A robot-assisted ultrasound examination system would provide other, not only ergonomic, benefits. For instance, since the location of the ultrasound transducer can be determined via the forward kinematics of the slave manipulator, three-dimensional ultrasound images can be reconstructed from a series of two-dimensional image slices. The process of creating three-dimensional ultrasound images from a series of two-dimensional slices has been suggested in lezzi et al., U.S. Pat. No. 5,551,432, which teaches a three-dimensional ultrasound imaging system that employs a motor with a screw drive to translate the ultrasound transducer in order to achieve images of the eye. U.S. Pat. No. 5,551,432 also describes an Auto-scroll feature that enables the operator to command the speed at which the transducer is translated. U.S. Pat. No. 5,810,008, Dekel et al., describes a three-dimensional ultrasound imaging system comprising position and orientation sensors that enable multiple planar computer images to be correlated to form three-dimensional ultrasound images. Another three-dimensional ultrasound imaging system that uses an actuator to move the ultrasound transducer is described in U.S. Pat. No. 5,759,153, Webler et al. Yet another three-dimensional ultrasound imaging system is described in U.S. Pat. No. 5,842,473, Fenster et al.
Remote probe positioning could also be used in teleradiology to examine patients at distant or inaccessible locations. Although a number of methods for transmitting ultrasound images have been proposed in the literature (Sublett, 1995), none allow the radiologist to view and manipulate the ultrasound transducer at the remote site. The remote positioning of an ultrasound transducer for endoscopic applications has been described in a number of patents. U.S. Pat. No. 5,842,993, Eichelberger et al., describes a navigable ultrasonic imaging probe assembly that can be positioned by the user endoscopically. Another endoscopic ultrasound transducer positioning system is described in European Patent application No. 0 514 584 A2, Solomon et al.
The computer-controlled positioning of an ultrasound probe has been described in other applications. For example, U.S. Pat. No. 5,836,880, Pratt, describes an animal tissue scanning system comprising a computer-positioned ultrasound transducer. However, such positioning has not been done as a function of sensed variables, such as ultrasound transducer position, forces or the image it acquires.
The control of multiple parameters for ultrasound image acquisition can be quite difficult. A control architecture suitable for controlling an ultrasound imager or other complex equipment is described in U.S. Pat. No. 5,853,367. The system is concerned with the efficient distribution of task loading for complex computerized systems.
The ability to position the ultrasound transducer in response to acquired ultrasound images would also be of benefit to image-guided interventions (e.g., percutaneous pericardial puncture) and registration with past examination records or images obtained with other imaging methods (e.g., MRI). The use of ultrasound imaging together with three-dimensional tracking of the transducer probe has been proposed in U.S. Pat. No. 5,797,849 as a tool for improving medical interventions.
A system for medical ultrasound is presented in which the ultrasound probe is positioned by a robot arm under the shared control of the ultrasound operator and the computer. The system comprises a robot arm design suitable for diagnostic ultrasound, a passive or active hand-controller, and at least one computer system to coordinate the motion and forces of the robot and hand-controller as a function of operator input, sensed parameters and ultrasound images.
While the ultrasound probe is positioned by a robot, the operator, the robot controller, and an ultrasound image processor have shared control over its motion. The motion of the robot arm and the hand controller of the proposed ultrasound are based on measured positions and forces, acquired ultrasound images, and/or taught position and force trajectories. Several modes of control are presented, including the control of the transducer using ultrasound image tracking.
An inherently safe, light, backdrivable, counterbalanced robot has been designed for carotid artery examinations but can be easily adapted for other examinations.
To operate the system, the ultrasound technician manipulates a hand-controller and enters commands via a user interface. The hand controller displacement and/or forces are sensed by appropriate sensors and read in by a computer that interprets these as a desired ultrasound transducer location or velocity or force or combination thereof (by location we mean position and orientation). A suitably designed mechanism, preferably a backdriveable, counterbalanced and light robot, positions the ultrasound transducer against the human body according to the above desired and possibly scaled values. The ultrasound transducer image is displayed on a monitor observed by the ultrasound technician, who can alter the ultrasound transducer location and force by manipulating the hand controller or entering commands via the operator interface. The operator can either control all degrees of freedom of the ultrasound transducer by manipulating the hand controller, or can control fewer degrees of freedom, with the remaining degrees of freedom being controlled by a computer. The computer-controlled degrees of freedom could specify a particular location or velocity trajectory, such as a probe translation or rotation motion, or a particular force, or the tracking of a particular feature in the ultrasound image acquired by the ultrasound machine, or a previously executed trajectory. To give the operator an intuitive way of controlling the forces the ultrasound transducer exerts on the human body, the hand controller could be active, i.e. have actuators that can exert a force on the ultrasound technician""s hand. These forces could be proportional to the ultrasound transducer forces.
The invention is directed to a method of positioning an ultrasound transducer onto the surface of a human body comprising: mechanically positioning the ultrasound transducer on the surface of the human body by an operator positioned remotely from the ultrasound transducer operating a hand controller which is linked to the ultrasound transducer and which by means of a programmed computer instructs and causes the ultrasound transducer to be positioned on the surface of the human body, the ultrasound transducer then acquiring and transmitting ultrasound images electronically to a display viewed by the operator.
The hand controller can control electronically and remotely the position of the ultrasound transducer on the human body, the velocity of the ultrasound transducer over the human body or the force exerted by the ultrasound transducer on the human body. The hand controller can control electronically and remotely the velocity and force of the ultrasound transducer on the human body. The hand controller can control only some of the degrees of freedom available to the ultrasound transducer.
The computer can be programmed to hold the ultrasound transducer at a fixed position on the human body, and the operator can be permitted to control orientation of the ultrasound transducer. The degree of force exerted by the transducer can be controlled by the computer according to a force sensor reading and the operator can be permitted to control orientation of the ultrasound transducer.
When normal force exerted by the transducer is controlled by the computer, the pitch of the ultrasound transducer can be adjusted to a stated program value in the computer. The hand controller can be a joy stick which can provide force and feedback to the operator.
The connection between the positioning of the ultrasound transducer and the operator and the hand controller can be performed by means of a counterbalanced robot. The program in the computer can control certain degrees of freedom and the counterbalanced robot can control other degrees of freedom.
The invention is also directed to a method of performing ultrasound on a person comprising using a robot arm to position an ultrasound probe on the surface of the person according to shared control of a remotely positioned ultrasound operator and a programmed computer, the ultrasound probe acquiring and transmitting ultrasound images to a display viewed by the operator.
The ultrasound transducer probe information can be displayed on the monitor, and the operator can activate the hand controller to regulate the force applied by the ultrasound transducer probe on the surface of the human body. The operator can control motion of the ultrasound transducer probe along certain degrees of freedom and the programmed computer can control the motion of the ultrasound transducer probe along other degrees of freedom.
The computer can be programmed to recall trajectories followed by the ultrasound transducer probe during a prior ultrasound scan of the human body. The computer can be programmed to recall serial positions and serial forces applied by the ultrasound transducer probe during a prior serial position and serial force trajectory followed by the ultrasound transducer probe on the human body.
The computer can be programmed to repeat scans of the ultrasound transducer probe from different incremental positions on the human body lateral to the scan direction and rationalize the repeated scans to generate a three-dimensional ultrasound image on the monitor.
The computer can be programmed to perform mixed modes of operation wherein the operator shares control of the position of the ultrasound transducer probe along certain axes with taught control programmed into the computer and a tracking mode along a plane is programmed in the computer while the operator controls the movement of the ultrasound transducer probe along the remaining degrees of freedom. Control of the position, force or velocity of the ultrasound transducer can be shared between the operator and the computer and determined according to the ultrasound image.
The operator can use an input device to input a component of motion control to the transducer to scan new parts of the human body and to input a component of orientation control to the transducer while observing the ultrasound images generated by the ultrasound image monitor to maximize image signal-to-noise ratio.
Ultrasound image features can be processed by the computer to determine the optimum orientation of the transducer and provide an automatic orientation control signal component which can be added to the attitude control input from the operator""s input device.
The transducer image features can be processed by the computer to provide an automatic direction control signal component which can track relevant anatomical structures under the surface of the skin of the human body.
The computer can sense the force vector applied by the operator to the input device and can scale the force up or down and add it to a predetermined force applied between the transducer and the human body. The input device can be capable of displaying a force vector to the operator that can be computed by the computer based scaling the actual force observed at the probe/skin interface of the human body.
The direction of motion of the transducer can be determined from a recording of a previous scan. The hand controller can be a joy stick which can provide force feedback to the operator.
The invention is also directed to an apparatus for positioning an ultrasound transducer onto a human body comprising: (a) a mechanism to position the ultrasound transducer on the human body; (b) a hand controller to enable an operator to input into a computer a desired position, a desired velocity or a desired force, or a linear combination thereof; (c) a computer control that maps the operator input into the ultrasound transducer position, velocity or force.
The hand controller can control the position of the transducer, the velocity of the transducer, the force of the transducer, or a linear combination of velocity and force of the transducer.
The hand controller can be a 6 degrees of freedom joy stick which can provide force-feedback to an operator of the apparatus. The joy stick might control only some of the degrees of freedom of the transducer.
The mechanism can be a counterbalanced robot. The robot can have a 4-bar linkage wrist. The apparatus can include a 6 degrees of freedom rate control device.
The invention is also directed to an apparatus for performing ultrasound on a person comprising: (a) a robot arm with an ultrasound transducer for positioning the transducer on the surface of the body of the person; (b) a passive or active hand controller which is operated by an operator to instruct the robot arm to position the ultrasound transducer on the surface of the body of the person; and (c) a computer which is programmed to coordinate motion and force of the robot and hand controller as a function of operator input, sensed parameters and ultrasound images.
The operator can control the apparatus in a master-slave mode, and the robot can track operator position, velocity or force. The hand controller can be passive or active.